Warming Up! (page 3)
The original experiment question was to see whether a high heat capacity meant good heat retention, therefore making a particular material a good candidate for use as a body warmer. My hypothesis was that a higher heat capacity would mean better heat retention and that a stone would have the highest heat capacity. The results of this experiment supported the hypothesis in multiple ways. Most of the materials' results showed that a higher heat capacity does mean better heat retention. Even though the stone did not have the highest heat capacity, it came in second place in the heat capacity test and had the 3rd highest heat retention. Baking soda, which had the highest heat capacity, had one of the lowest results for heat retention. However, it is reasoned that this still doesn't counter the hypothesis because the baking soda results could have been incorrect: the baking soda was white and white substances have a greater potential for error with the IR thermometer. The erratic timeline for the baking soda's retention results support this explanation. Overall, while the data from this experiment generally support the hypothesis, more materials would need to be tested to have conclusive results.
Most of the results in the heat capacity portion of the experiment were as expected. Most of the solids used in the experiment demonstrated a higher heat capacity than the liquids and it is expected that this will show again if further testing is conducted. However, the experiment also gave several unexpected results. For one, the baking soda had the highest heat capacity exceeding even that of the stone. This is most likely because it was packed tightly in the tin, making it almost like the stone. Also, the salt had the lowest heat capacity when, being a solid, it was expected to have one of the higher heat capacities. As mentioned above, however, both of these materials are white in color, possibly affecting their results. Ink was used to darken the materials and make results more accurate but even having done that, the potential for error is higher than that of the other materials.
As expected, there is definitely a connection between a material's heat capacity and its heat retention qualities. Based on the small sample used in this experiment, one can conclude that a higher heat capacity would mean better heat retention. There were also several other interesting results in the experiment. For one, while they were very close, the liquids had a higher average drop in temperature over 30 seconds. Another interesting fact is that the salt, stone, small gravel, and sand all continued to get hotter even after they were removed from the heat source, as seen in the heat retention temperature graph. The same graph also shows that these items then went on to have generally steeper temperature declines than those whose temperature did not increase post-heating. An interesting fact is that the sand and small gravel both had temperature declines after the tenth minute that were much sharper than those of the other materials.
Practicality and Use as a Warmer
The real-life side of this experiment was the possibility of using the natural test materials as warmers instead of commercial, chemical products. To look into the practicality of such use, a graph (see in results) was created showing the heating speeds of the materials. This is important because most commercial warmers act instantaneously or need to be heated for just a few minutes. The graph shows that most of the items with high heat capacities and good heat retention qualities take longer to initially heat. While all of the samples reached the target temperature of 70°C or 343.15 Kelvins within 2 minutes, 45 seconds, the samples were only 50 grams each, not even enough to fully fill a muffin tin. While a larger amount of material would have better heat retention qualities, it would have to be heated for longer amounts of time and be bulky, particularly with the stone, making it impractical as a warmer. If a user is unconcerned about size, however, larger amounts of material could be used for a warmer if it wouldn't be movable such as one for use overnight. Overall, while the samples do have the theoretical potential to be used as warmers, none of them are small or practical enough to allow them to be compared to commercial warmers.
Explaining the Results
Density offers an explanation for the heat capacity results. The table below shows the densities of the test materials used. Salt can be excluded because of the potential for error with the infrared thermometer. Then, with the exception of the small gravel and water, the materials show that a higher density means a higher heat capacity. The heat retention qualities of the gravel can be explained by the way the loose rocks had gaps in them, allowing airflow and cooling on all sides rather than just the top as with the other liquids. Another possible scientific explanation for the heat capacities of materials is their molecular arrangement. Heat capacity is the measure of how much energy is needed to raise the temperature of a substance by 1 Kelvin and heat is caused by vibrations in the atoms and molecules of a substance. Therefore, heat capacity can be expressed as the energy needed to cause these molecules and atoms to move and vibrate faster. In a solid, the molecular arrangement is usually tighter, with more bonds between the molecules. Because of this, it can be reasoned that it would be harder to move the molecules of a solid, meaning it would need more energy to raise its temperature (a higher heat capacity). In liquids, where the molecular arrangement is more loose and random, there are less bonds between the molecules, meaning it would take less energy to move them, hence a lower heat capacity.
There were several things that could have been done to improve the experiment. One limitation was the amount of samples that was tested; more samples would have allowed for a more conclusive verdict. A potential source of error in the experiment was the infrared thermometer. The batteries ran out and were replaced during the experiment, which may have affected the results. A more expensive thermometer would have most likely offered more precise readings. If this experiment was repeated, more measures would be taken to overcome the white color problems. Another piece of more expensive equipment that could have been used is a calorimeter, which could have given more accurate results.
The data from this experiment gave rise to many new research questions that can lead to follow-up experiments. One of these would be to see if or how density affects heat capacity. In the experiment, the denser items such as the stone and baking powder had higher heat capacities than less dense items such as the loose gravel or the water. Another question that comes up relates to why some of the items continued to heat up after they were removed from the heat source. This is particularly interesting because it happened with only some of the test samples.
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